SysfsIOT transformer

An instance of MonadSysfs which runs MonadSysfs operations in IO. This instance must be run on an actual Linux sysfs GPIO filesystem and will fail in any other environment.

Interactions with threads

Some parts of this implementation use the Haskell C FFI, and may block on C I/O operations. (Specifically, pollFile will block in the C FFI until its event is triggered.) When using this implementation with GHC, you should compile your program with the -threaded option, so that threads performing these blocking operations do not block other Haskell threads in the system.

Note that the C FFI bits in this implementation are marked as interruptible, so that, on versions of GHC later than 7.8.1, functions such as throwTo will work properly when targeting a Haskell thread that uses this implementation.

(On Haskell implementations other than GHC, the threading implications are unknown; see the implementation's notes on how its threading system interacts with the C FFI.)